Genetic interactions between repeated sequences in yeast will be examined. Methods are being developed to use yeast as an experimental system to study the mechanism of gene amplification. The resistance gene for the antibiotic kanamycin has been introduced into a yeast chromosome by transformation. Resistance to increasing concentrations of the antibiotic will be used to recover amplified units. The role of DNA replication and recombination in the amplification process will be examined through the use of mutant yeast strains. Mutants that have elevated levels of intrachromosomal gene conversion, a process that maintains sequence homogeneity in multigene families, will be isolated. The effect of these mutants on different recombination processes will be examined. The mechanism of chromosome pairing will be studied through the use of different constructions using duplications and deletions. Multiple gene conversions in a tandem array will be studied to see if the events are independent or concerted. The regulation of rapid sequence changes in multigene families can be studied in this way. The role of transposable elements in influencing the direction of gene conversion in multigene families will be examined. Directional conversion resulting from initiation at adjacent transposable elements will help in understanding the mechanisms in the evolution of multigene families. Mutants deficient in sister chromatid exchange will be isolated to determine how this recombinational process differs from those that operated on homologous chromosomes.